HR: 0800h
AN: B51C-0966    [Abstracts]
TI: Impacts of Canopy Structure on Water, Energy and Carbon Exchange in a Loblolly Pine Forest in Southeast USA
AU: * Song, C
EM: csong@email.unc.edu
AF: University of North Carolina at Chapel Hill, Department of Geography CB# 3320, Chapel Hill, NC 27599 United States
AU: Band, L E
EM: lband@email.unc.edu
AF: University of North Carolina at Chapel Hill, Department of Geography CB# 3320, Chapel Hill, NC 27599 United States
AU: Randolph, A
EM: tonyrand@email.unc.edu
AF: University of North Carolina at Chapel Hill, Department of Geography CB# 3320, Chapel Hill, NC 27599 United States
AU: Oren, R
EM: ramoren@duke.edu
AF: Duke University, Nicholas School of Environment, Durham, NC 27708 United States
AU: Katul, G
EM: gaby@duke.edu
AF: Duke University, Nicholas School of Environment, Durham, NC 27708 United States
AB: Forest ecosystems play a key role in water, energy and carbon exchange between the terrestrial ecosystems and the atmosphere. One of the major factors that govern the rate of exchange of these fluxes is canopy structure. However, most ecosystem models simulating water, energy and carbon exchange of forest ecosystems with the atmosphere are based on a simplified canopy structure, where the forest canopy is assumed to be a turbid medium with leaves uniformly distributed within the canopy as particles of infinitesimal size, and light propagates through the canopy following an exponential decay. In reality, there are gaps of various sizes within the forest canopy. Lights passing through the gaps are not attenuated creating sunflecks on the forest floor. In this study, we represent the canopy of a loblolly pine stand as an assembly of individual crowns with gaps between and within the crowns. Gaps in the canopy are estimated based on statistics of canopy structure. Such a representation of canopy structure relinquishes the need for the sizes and locations of each tree as are needed in three-dimensional radiation transfer models, making it possible to account for the landscape canopy structure in ecosystem models. The loblolly pine stand is located in the Blackwood Division of Duke Forest, and is an AmeriFlux site where water, energy and carbon exchanges with the atmosphere have been monitored with eddy-covariance instruments since 1997. We simulated the exchanges of these scalars using the RHESSys model with gaps in the canopy estimated from the statistics of canopy structure. Comparision with data from the eddy-covariance instruments shows that replacing a turbid medium canopy with a gapy canopy in RHESSys significantly improved simulation of these fluxes through the forest ecosystem on a daily and weekly time scale. The results identify improper canopy representation in models as a source of uncertainty in estimates of regional water, energy and carbon cycles of the terrestrial ecosystems and suggest a convenient approach to improve the accuracy of these estimates.
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting